Halo: Reach's online multiplayer along with a retooled campaign level for Firefight mode. Halo: CE Anniversary will not support Xbox Live multiplayer whatsoever (outside of co-op). These maps are for loading into Halo: Reach (think: ODST), according to comments made by 343 Industries' Frank O'Connor on Spike TV. He also said it will be a budget-priced game.
Hit the jump for the teaser trailer shown during Microsoft's E3 2011 press conference.
Update: O' Connor clarified with Joystiq that Anniversary's multiplayer component, while employing the Reach engine, will still be playable on the Anniversary disc itself. The game will also include a voucher to download the maps for play within Halo: Reach.